Antibiotic, which is bacteriostatic among the following is

Tetracycline

The correct answer is option 3. Tetracycline.

Let us delve deeper into each antibiotic and their mechanisms of action to understand why Tetracycline is classified as bacteriostatic.

1. Aminoglycosides

Examples: Gentamicin, Streptomycin, Neomycin

Mechanism of Action: Aminoglycosides are bactericidal antibiotics that work by binding to the 30S ribosomal subunit of the bacterial ribosome. This binding interferes with protein synthesis by causing misreading of mRNA, which results in the production of defective proteins. This disruption ultimately leads to bacterial cell death.

Key Point: The damage to bacterial ribosomes and the resulting errors in protein synthesis are typically lethal to bacteria, hence these antibiotics are considered bactericidal.

2. Ofloxacin

Examples: Ofloxacin, Ciprofloxacin, Levofloxacin

Mechanism of Action: Ofloxacin is a fluoroquinolone antibiotic. Fluoroquinolones inhibit bacterial DNA gyrase and topoisomerase IV, enzymes essential for DNA replication and repair. Inhibition of these enzymes leads to the accumulation of DNA damage, ultimately causing bacterial cell death.

Key Point: By causing irreversible damage to bacterial DNA, fluoroquinolones are classified as bactericidal.

3. Tetracycline

Examples: Tetracycline, Doxycycline, Minocycline

Mechanism of Action: Tetracycline is a bacteriostatic antibiotic. It works by binding to the 30S ribosomal subunit of the bacterial ribosome, inhibiting protein synthesis. This prevents bacteria from producing essential proteins needed for growth and reproduction.

Key Point: While tetracycline inhibits bacterial growth, it does not kill the bacteria directly. The bacteria remain alive but unable to proliferate. The immune system eventually clears the inhibited bacteria.

4. Penicillin

Examples: Penicillin G, Penicillin V, Amoxicillin

Mechanism of Action: Penicillin is a bactericidal antibiotic. It inhibits bacterial cell wall synthesis by interfering with the transpeptidation enzyme that cross-links peptidoglycan layers in the bacterial cell wall. This leads to cell lysis and death.

Key Point: By compromising the structural integrity of the bacterial cell wall, penicillin causes bacterial cells to burst and die.

Summary:

Bacteriostatic Antibiotics: Inhibit bacterial growth and replication but do not kill bacteria directly. They rely on the host’s immune system to eliminate the inhibited bacteria. Tetracycline is a classic example of a bacteriostatic antibiotic, as it prevents protein synthesis without directly causing bacterial death.

Bactericidal Antibiotics: Directly kill bacteria. Examples include Aminoglycosides (which cause errors in protein synthesis leading to cell death), Ofloxacin (which damages bacterial DNA), and Penicillin (which destroys bacterial cell walls).

Thus, Tetracycline is classified as bacteriostatic because it inhibits bacterial growth and reproduction, allowing the host’s immune system to eventually clear the infection.

The correct answer is: 3. Tetracycline.